1. Field of the Invention
The present invention relates to a resistor device, and more particularly, to a thin-film resistor fabricated on a semiconductor wafer displaying superior performance and higher stability.
2. Description of the Prior Art
In semiconductor integrated circuit designs, a simple resistor is often made from a gate conductive layer or an impurity-doped layer in a predetermined area of the semiconductor wafer. However, the resistance typically obtained from the gate conductive layer and the impurity-doped layer is often insufficient. One approach to increase the resistance is to design a larger surface area of the resistor. However, it is undesirable to make this resistor device having a large surface area in a highly-integrated ULSI product. Furthermore, the resistance of the silicon-containing gate conductive layer and impurity doped layer varies with temperature changes, which results in instability of the resistance values. Therefore, there is a need for fabricating a stable thin-film resistor with lower conductivity on a semiconductor wafer.
Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are cross-sectional diagrams schematically showing a method of forming a resistor 20 on a dielectric layer 12 according to the prior art. As shown in FIG. 1, a resistor 20 is produced by first sequentially forming a resistance layer 14 and a protective layer 16 on the surface of the dielectric layer 12. The resistance layer 14 and the protective layer 16 are defined by conventional photolithographic and etching processes. A conductive layer 18, made of an aluminum alloy, is then formed on the protective layer 16. As shown in FIG. 2, a large portion of the conductive layer 18 and the protective layer 16 positioned on the resistance layer 14 is removed by a wet-etching process. The remaining portion at the two ends of the resistance layer 14 functions as two electrical terminals for the two ends of the resistance layer 14.
The wet-etching process is an isotropic etching process with equal horizontal and vertical etching depths. To define the conductive layer 18 properly through wet etching, the surface area of the resistance layer 14 and the protective layer 16 must be large. Only if the resistance layer 14 and protective layer 16 is large can a large portion of the conductive layer 18 and protective layer 16 be removed while still preserving the two portions at the ends of the resistance layer 14. Although this method can be utilized in processing gate widths greater than 3 micrometers, it is ineffective in processing narrower gate widths.
It is therefore a primary objective of the present invention to provide an improved thin-film resistor with much more stable resistance and a smaller required surface area.
In accordance with the objective of the present invention, the present invention provides a thin-film resistor on a dielectric layer of a semiconductor wafer. The thin-film resistor has a dielectric layer deposited on the semiconductor wafer. A patterned resistance layer is formed on the dielectric layer. A buffering layer is formed on the resistance layer, the buffering layer comprising two openings above two opposite ends of the resistance layer. A protective layer is positioned on the buffering layer and comprises two openings above the two openings of the buffering layer. An insulating layer covers the upper and side surfaces of the protective layer, the side surface of the buffering layer and the resistance layer, and the dielectric layer. The insulating layer has two openings above the two openings of the protective layer. Two conductive layers are positioned in the two openings of the buffering layer, the protective layer and the insulating layer, and are in contact with the two ends of resistance layer. The conductive layers are used as two electric terminals for electrically connecting to the two ends of the resistance layer.
It is an advantage of the present invention that the thin-film resistor thus formed comprises a resistance layer below a buffering layer and a protective layer. The buffering layer buffers the thermal stress exerted on the resistance layer, and the protective layer protects the resistance layer from plasma damage. The resulting thin-film resistor has a much more stable resistance.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.